Reverse battery protection is a critical part of the automotive circuitry and electronics which must be protected from, for example, the accidental connection of the vehicle battery in the wrong polarity, as this would destroy most semiconductor chips used in the vehicle including, for example, the chips used in actuators.
Reverse battery protection in low current application circuits generally involves the use of a diode which allows current to flow in only one direction. The use of a diode has the benefit of not only protecting a circuit from an accidental reversal of battery polarity but also has the benefit of preventing a circuit's storage capacitor(s) from being discharged during battery dropouts or other common disturbances on the power supply. A disadvantage associated with the use of diodes, however, is the resultant drop in voltage (approximately 0.6V) which occurs across the diode. While this drop in voltage is insignificant in low current applications, it becomes problematic in high current applications where a large power drop across a diode can lead to overheating. This of course can be a significant issue in, for example, high temperature applications where the circuit semiconductors are already operating close to their maximum allowable junction temperatures.
Metal-oxide-semiconductor field-effect transistors (MOSFETs) have also been used in circuits for reverse battery protection. While the use of a MOSFET overcomes the issue of overheating, MOSFETs are not capable of providing any directional current flow control in the event of, for example, a very rapid discharge of a circuit's storage capacitors during, for example, dropouts or other disturbances to the power supply. In many high temperature applications, low voltage drop (and power dissipation) of the MOSFET coupled with the unidirectional flow control of the diode are both desired features.
The present invention is directed to a reverse battery circuit operable at high temperatures and tolerant of load dump pulses in excess of 200V.